1. Field of the Invention
This invention relates to a method of producing a thin film resistor having a specific shape by etching a thin film resistive layer and a barrier metal layer deposited on a substrate.
2. Description of the Related Art
A thin film resistor is conventionally formed on a semiconductor device, especially on an integrated circuit (IC) chip through an insulating film, to achieve size reduction and cost reduction of the device. The thin film resistor is generally made of CrSi system material having a small thermal coefficient of resistance (TCR) such as CrSi or CrSiN.
FIGS. 8A-8D show a manufacturing process for such a thin film resistor in a stepwise manner in a case where the thin film resistor is made of CrSiN. Specifically, an insulating isolation film and circuit elements (not shown) such as MOSFETs and bipolar transistors are formed on a single crystal silicon substrate 1 by a well-known method. Then, as shown in FIG. 8A, a silicon oxide film 2 as an intermediate insulating film is deposited on the silicon substrate 1 by chemical vapor deposition (CVD) method, and a heat treatment is carried out to improve characteristics of the silicon oxide film 2. The silicon oxide film 2 secures an insulating property between the circuit elements and metallic wiring patterns.
After that, a CrSi system film 3 as a thin film resistive layer is deposited on the silicon oxide film 2, and a TiW film 4 as a barrier metal layer is deposited on the CrSi system film 3. A photoresist layer 5 is disposed on the TiW film 4 and is patterned into a specific shape. The TiW layer 4 is etched by a well-known wet etching method using the photoresist layer 5 as a mask to expose the CrSi system film 3 as shown in FIG. 8B. Next, as shown in FIG. 8C, the CrSi system film 3 is patterned by a plasma dry etching method using the stack of the photoresist layer 5 and the TiW film 4 as a mask. This method is disclosed in, for example, JP-A-7-335831. After that, the photoresist layer 5 is removed, and as shown in FIG. 8D, electrode wiring patterns 6 are formed through a well-known photo-lithography treatment. The electrode wiring pattern 6 is made of, for example, aluminum. Consequently, the thin film resistor formed from the CrSi system film 3 is provided.
In the manufacturing process described above, however, when the TiW film 4 as the barrier metal layer is etched, etching residues are readily produced and side etching is liable to occur in a lateral direction under the edge portion of the photoresist layer 5. When an initial pattern dimension of the photoresist layer 5 (see FIG. 8A) is d1 and a side etching width of the TiW film 4 is .DELTA.d, the TiW film 4 remains between the CrSi system film 3 and the photoresist layer 5 with a dimension d2 (=d1-2.DELTA.d) that is shorter than d1 by 2.DELTA.d. As a result, dispersion in processing width of the TiW film 4 is increased, so that processing accuracy of the thin film resistor is lowered.